彩 is a bound form (b.f.) that appears as the first or second element in compound words. Its core meanings are 'color' (彩色, 彩灯), 'brilliance/splendor' (精彩, 光彩), and 'prize/winnings' (彩票, 中彩). A rare sense is 'blood from a wound' (挂彩). Because it is a bound form, it never stands alone as a word; you must attach it to a root.